The present invention relates to equipment for radiologically examining a patient and, in particular, to radiological examination with a relatively narrow band of wavelengths.
Radiological examination of a patient can be performed with the familiar x-ray machine. A conventional x-ray photograph provides an image by detecting the different absorbing characteristics of tissues. However, this equipment operates over a relatively wide band of wavelengths so that its resolution and contrast are rather limited. Another disadvantage of conventional x-ray radiology is the need to work with photographic film. In addition to being expensive, such film requires dark room treatment and has a relatively slow, logarithmic response.
In a known radiological technique, a dye injected into a patient has a distinctive appearance on an x-ray photograph. The dye, when infused into the relevant tissue, adds contrast and reveals internal structure which would normally be lost under x-ray examination. However, these dyes often provide insufficient resolution to determine precise positions and concentrations. The specific absorption characteristic of a target or dye atom may exhibit a distinctive absorption feature only over a relatively narrow region (e.g., 100 to 200 eV) of its spectrum. Therefore, in order to study the behavior of this atom radiologically it would be advantageous to use only wavelengths in this energy region for optimum resolution and minimum exposure to the patient.
As an example of varying absorption spectra, the different valences of gold (Au.sup.+ Au.sup.+++ and Au) have distinctively different spectra, characteristic of the valence. It will be understood, therefore, that proper selection of a stain and the relevant energy range may indicate not only the presence or absence of the radiation absorbing stain, but also the mode of interaction between the atom and the tissue under examination.
A somewhat limited but so far the only method of determining molecular structure in a patient is radiating a sample with radio frequency waves to determine its nuclear magnetic resonance. Depending upon the spin characteristics of the target molecules, radio waves are absorbed and retransmitted in a characteristic pattern of wavelengths.
The literature also discusses absorption spectroscopy. For example, P. A. Lee and J. B. Pendry, Phys. Rev., Vol. B11, p. 2795 (1975); E. A. Stern, Phys. Rev., Vol. B10, p. 15 (1974); G. S. Brown and S. Doniach, The Principle of X-ray Absorption Spectroscopy, Synchrotron Research, Edited by H. Winick and S. Doniach, p. 353, Plenum Press (1980).
A known monochromator crystal can be positioned and bent to affect the wavelengths of reflected radiation. This principle operates in accordance with the well known Bragg's Law, which provides: 2d sin .theta.=n.lambda. wherein .theta. is the angle of reflection with respect to normal, .lambda. is the wavelength, n is an integer and d the effective repetitive spacing of the crystal lattice. Regarding the bending of a crystal, see T. Matsushita and R. P. Phizackerly, Japanese J. Appl. Phys., Vol. 20, p. 2223 (1981).